Contents

Overview

After reading this section, you should have a basic understanding of how the ACE appliance selects a real server for a client request using a predictor and how to configure a hash header predictor as an example.

When there is a client request for web services, the ACE selects a server that can successfully fulfill the client request in the shortest amount of time without overloading either the individual server or the server farm.

The ACE makes load-balancing choices using a predictor. When you configure a predictor, you define the series of checks and calculations that the ACE will perform to determine which real server can best service a client request.

For each server farm, you can configure one of several predictor types to allow the ACE to select an appropriate server. Two common predictor types include the following:

Round-robin—Selects a server from the list of real servers based on weighted server capacity. A weight can be assigned to each real server based on its connection capacity in relation to the other servers in a server farm. Servers with higher weight values receive a proportionally higher number of connections than servers with lower weight values. For example, a server with a weight of 5 would receive five connections for every one connection received by a server with a weight of 1. Also known as weighted round-robin, this is the default predictor.

Hash header—Selects a server using a hash value based on the HTTP header name.

You can configure a server load-balancing predictor by following these steps:

1. Choose a server farm.

2. Choose a predictor type and its parameters.

3. Deploy the configuration.

This section describes how to configure a hash header predictor for the server farm that was created in Configuring Server Load Balancing (as illustrated in Figure 6-1). You can use either the ACE Device Manager GUI or the CLI.

Configuring a Hash Header Predictor Using the Device Manager GUI

You can configure a hash header predictor using the ACE Device Manager GUI by following these steps: